Improve README and place quick help content as a button in toolbar

[ugurdogrusoz]

Let's improve the README as follows:

• Move the screenshot on loading the extension to the appropriate section (screenshot itself could be improved?)
• Talk about the major use cases under Usage with a screenshot for showing a sample map of the browse history as a map

Let's combine information page and how to page under Settings and put under a new dialog opened with a new button in the toolbar (use ? icon for this).